In the production of plastic containers, in general not reusable, in the form of bottles, phials and the like, the problem of the difficulty of eliminating said containers once emptied because of their physical dimensions or their polluting characteristics is becoming more acute because of their poor degradability in time.
On the other hand these containers require rigidity sufficient for good stability and easy handling in use, transportation and storage.
This cannot be secured without a certain wall thickness and the resulting relatively high quantity of material, which reflects negatively on the product cost.
In the know art have been proposed composite bottles, i.e. formed of a relatively yielding plastic containing an element inserted in a more rigid supporting structure.
For example, in French patent application FR-A-2 166 173 is shown a substantially cylindrical composite container consisting of a rigid external tube in which is fixed a plastic receptacle. The receptacle of such a container must however have relatively thick walls. Otherwise the receptacle would tend to fold back on itself, slipping into the stiffening tube. In addition, during pouring, the receptacle would slip easily out of the tube due to the the weight of its contents.
In French patent application FR-A-2 013 654 there is proposed a container substantially similar to the above with the only variant being that the side wall of the cylindrical receptacle has projections for engagement with corresponding holes in the external supporting shell.
Although this embodiment ensures better fixing between the shell and the receptacle, when the latter is full or under pressure a rather high rigidity of the receptacle walls is still necessary to prevent collapsing or slipping out during pouring or when it is partly empty. In effect, the container described in said patent has its utility simply in the greater resistance to internal pressure given by the spherical bottom of the receptacle while the cylindrical external shell serves only to provide the container with a flat resting base.
In addition to wasting plastic material, the need for using receptacle with relatively rigid walls results in the difficulty of folding the container once emptied to reduce its space occupied and facilitate its disposal.
In U.S. Pat. No. US-A-4 456 334 are shown various solutions in which the cylindrical bottles are formed to have a containing part supported by a rigid part. The containing parts are readily folded either because made of very thin and easily deformed plastic material or due to the presence of bellows or the like. With bellows, the expenditure for plastic material is great while with thin walls the supporting part made at the same time of plastic is particularly complicated and costly and hence unsuited for a single us.